1. Field of the Invention
The present invention relates in general to slab style gate valves and, in particular, to a shear gate valve having a valve seat with a deformable inner sleeve.
2. Brief Description of Related Art
A production bore intervention valve may be used on a subsea oil and gas work over riser system. The work over riser system provides safe access to the production bore during well intervention activities. The intervention valve provides a means to control well bore fluids and also to allow the platform to disconnect from the well during an emergency situation. Closure of the valve may be required when downhole tooling such as coiled tubing or wireline are still running through the valve. The valve must be capable of severing the coiled tubing or wireline to allow the valve to close, while maintaining the valve's function as a fluid barrier.
A typical gate valve used in connection with oil and gas production has a body with a flow passage extending through it. The flow passage intersects a central cavity. Seat rings or seats are placed in counterbores formed in the flow passage at the intersection of the flow passage with the cavity. A gate will variably move through the central cavity. to block the flow passage. The seats bridge a gap between the valve body and the gate to prevent fluid from flowing around the gate when the gate blocks the flow passage.
The action of shearing any downhole tooling requires significant loads and very high localized stresses on the gates and seats involved. This stressing can lead to damage or general degradation of the surface finish on any of the sealing faces of the gates and seats adjacent to the edges where this shearing occurs. This surface damage to the sealing faces of the gate and the seat can cause sealing problems when the valve is closed, leading to leakage. Currently there are issues with the sealing of gate valves after shearing of coiled tubing, wireline, or a combination of both. As the movement of the gate presses the wireline or coiled tubing against the valve seat, the sealing faces of the valve seat adjacent the gate and interior of the valve may significantly deteriorate. A protective barrier may be placed between the seat and the wireline or coiled tubing to limit the damage to the seat; however, these barriers may become misaligned during operation and interfere with the seats ability to seal to the gate. Even seemingly minor damage to the surfaces of the gate and seats is enough to have an effect on the ability of the valve to seal. Therefore a valve seat with a protective barrier that does not inhibit or prevent sealing of the seat to the gate during use would be beneficial.